Described below is a method for generating intensive high-voltage pulses and for the industrial use of these high-voltage pulses and an associated circuit arrangement for carrying out the method.
Intensive high-voltage pulses are used for numerous industrial processes. For example,                in construction engineering, building materials are made accessible for quality analysis by an electrohydraulic material breakdown such as, e.g., concrete or asphalt, or        building materials such as, e.g., reinforced steel concrete are recycled by shockwave-based, i.e. electrohydraulic methods.        
Other possible uses of intensive high-voltage pulses as a part of industrial applications are, for example,                in biotechnology, in which cell proteins, DNA or other cell content or cell wall components are extracted from biological cells by electroporation of the cell walls, or        in environmental technology in which, e.g., slurry is preprocessed by electroporation in order to control putrefaction processes better by this means.        
Other possible fields of use of high-voltage pulses are found in the treatment or sterilization of agricultural products, particularly for eliminating animal and fungal damage by destroying the cell bond due to the high electrical fields on the outer skin of the agricultural products when these are brought into an area of sufficiently high electrical field strength (reactor).
The above applications in the use of high-voltage pulses are addressed partially in publications by Schultheiss et al. “INDUSTRIAL-SCALE ELECTROPORATION OF PLANT MATERIAL USING HIGH REPETITION RATE MARX GENERATORS”, Proceedings IEEE Pulsed Power Conference, 2002 and “OPERATION OF 20 HZ MARX GENERATORS ON A COMMON ELECTROLYTIC LOAD IN AN ELECTROPORATION CHAMBER”, Proceedings IEEE Power Modulator Symposium, 2003.
Such applications typically require pulse amplitudes of some 100 kV at current intensities of some 10 kA with pulse rates of some 10 pulses per second (pps) in continuous operation. In methods used industrially, a maintenance-free plant life of some 100 million pulses is essential for the economic running of such plants.
To produce the high field strengths necessary, high-voltage pulse generators according to the Marx principle are used, corresponding to the prior art, in which capacitors are charged up in parallel but are connected in series by suitable switches for generating pulses which is shown as prior art in FIG. 1 and will be described in detail below.
The main problem in the generation of pulses is the switches needed for it, in most cases gas-filled spark gaps, and their selective triggering with high accuracy over the entire life.
In a known solution of the problem, spark gaps are used for the switches which are designed in such a manner that they should achieve a life of over 100 million pulses. First solutions to the problem exist for Marx generators with electronic switching elements in accordance with the publication by Kirbie et al. “All-Solid-State Marx Modulator with Digital Pulse-Shape Synthesis”, report No. LA-UR-05-0631, Los Alamos National Laboratory, Los Alamos, N. Mex., USA 2005. However, the latter solutions to the problem do not yet achieve sufficiently high currents for industrial use.
According to the publication by Schultheiss et al., “Wear-less Trigger Method for Marx Generators in Repetitive Operation”, Proceedings IEEE Power Modulator Symposium, 2003, the gas discharge switches used hitherto for Marx generators in repetitive operation are in most cases used untriggered in such a manner that the spacing of the spark gap electrodes of the first Marx generator stage has a somewhat smaller spacing than that of the other stages; as a result, the breakdown voltage of these spark gaps is slightly less than that of the following ones and the first stage arcs through as the first one. As a result, an overvoltage of almost 100% of the charging voltage is generated at the second spark gap, as a result of which the second stage also arcs through. Analogously, the following stages then also arc through until the entire Marx generator is raised up and generates a corresponding pulse at the output.
To achieve a greater total current and thus a higher total power, it is often necessary to operate a number of such systems in parallel. However, this requires, in particular, synchronizing the time of pulse generation of the individual Marx generators with high accuracy in time. This synchronization is also necessary for an individual system if good control of the operating parameters is required for the desired process. Synchronization is generally effected by the fact that the ignition of the spark gap of the first stage does not occur by exceeding the ignition voltage during the charging process but this spark gap is deliberately ignited. There are several possibilities available for this ignition:                plasma cross triggering (Trigatron)        longitudinal plasma triggering        longitudinal overvoltage triggering        laser triggering.        
Both plasma cross triggering and longitudinal plasma triggering have hitherto not displayed sufficiently long lives. Laser triggering requires very high equipment expenditure and costs with limited life of the spark gap and is therefore used in most cases only for single pulse operation in very large research installations.
Longitudinal overvoltage triggering is the most suitable method. However, there has hitherto not been any practice-oriented device having sufficiently good characteristics and an adequate life. WO 2004/100371 A1 discloses a triggering/ignition device in a Marx generator having step capacitances and an associated operating method for this device. In the method for generating high-voltage pulses applied there, the Marx generator is triggered with high-voltage pulses, the trigger pulses being coupled in serially-inductively.
In practice, the solution described above provides neither a sufficiently high trigger quality nor an adequate life. It is based on inductively coupling a voltage pulse into the charging inductance at the ground end of the first Marx stage (pulse transformer) which is generated in an auxiliary winding (primary winding) by electronically interrupting a current with the aid of semiconductor switches. In this arrangement, the energy necessary for generating the overvoltage and igniting the spark gap must be temporarily stored in the winding on the primary side of the pulse transformer which leads to very unfavorable design criteria of this arrangement. Furthermore, the opening electronic switching element is in most cases an IGBT at the instant of pulse generation in the open state, as a result of which it is very sensitive to reactions from the Marx generator, particularly to overvoltages.
In general, the latter leads to such a circuit having a limited life which is not sufficient for industrial use. Furthermore, it is very difficult to scale this principle since great compromises have to be made with regard to conflicting requirements. For example, the provision of sufficiently high pulse energies for reliable ignition of the spark gap requires high self-inductance of the primary winding, whilst the requirement for great steepness of the pulse generated in this manner requires an inductance which is as low as possible.